Docker Swarm is Docker's native container orchestration tool for managing container clusters across multiple hosts. Key concepts include: Node (nodes, divided into Manager and Worker), Service (service, defining desired state), Task (task, a unit of work for a service), Stack (stack, a group of related services). Common commands: docker swarm init (initialize cluster), docker swarm join (join cluster), docker service create (create service), docker service scale (scale service), docker stack deploy (deploy stack). Swarm provides load balancing, service discovery, rolling updates, and other features.